[PATCH 3/4] x86: Adjust arch LBR CPU policy

[ngoc-tu.dinh@xxxxxxxxxx]

From: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>

Allow virtual arch LBR with a single depth that's equal to that of the
host. If this is not possible, disable arch LBR altogether.

Signed-off-by: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
---
 xen/arch/x86/cpu-policy.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index cf6b212fb6..2ac76eb058 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -638,6 +638,36 @@ static void __init calculate_pv_max_policy(void)
     p->extd.raw[0xa] = EMPTY_LEAF; /* No SVM for PV guests. */
 }
 
+/*
+ * Allow virtual arch LBR with a single depth that's equal to that of the
+ * host. If this is not possible, disable arch LBR altogether.
+ */
+static void adjust_arch_lbr_depth(uint32_t fs[FEATURESET_NR_ENTRIES])
+{
+    uint64_t host_lbr_depth;
+    bool lbr_supported = true;
+
+    rdmsrl(MSR_IA32_LASTBRANCH_DEPTH, host_lbr_depth);
+    if ((host_lbr_depth == 0) ||
+        (host_lbr_depth % 8) ||
+        (host_lbr_depth > 64))
+        lbr_supported = false;
+
+    host_lbr_depth = 1ul << ((host_lbr_depth / 8) - 1);
+    if ((host_lbr_depth & fs[FEATURESET_1Ca] & 0xff) == 0)
+        lbr_supported = false;
+
+    if (lbr_supported)
+    {
+        fs[FEATURESET_1Ca] = (fs[FEATURESET_1Ca] & ~0xffu) | host_lbr_depth;
+    }
+    else
+    {
+        __clear_bit(X86_FEATURE_ARCH_LBR, fs);
+        fs[FEATURESET_1Ca] = fs[FEATURESET_1Cb] = fs[FEATURESET_1Cc] = 0;
+    }
+}
+
 static void __init calculate_pv_def_policy(void)
 {
     struct cpu_policy *p = &pv_def_cpu_policy;
@@ -760,6 +790,9 @@ static void __init calculate_hvm_max_policy(void)
             __clear_bit(X86_FEATURE_XSAVES, fs);
     }
 
+    if ( test_bit(X86_FEATURE_ARCH_LBR, fs) )
+        adjust_arch_lbr_depth(fs);
+
     /*
      * Xen doesn't use PKS, so the guest support for it has opted to not use
      * the VMCS load/save controls for efficiency reasons.  This depends on
-- 
2.43.0



Ngoc Tu Dinh | Vates XCP-ng Developer

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